Light-emitting diodes based on InGaAlP can be produced by variation of the Al proportion with emission in a wide spectral range from red to yellow-green. By changing the Al content, the band gap of the InGaAlP system can be tuned from 1.9 eV to 2.2 eV.
During the operation of such light-emitting diodes, a decrease in the light power is observed depending on the operating conditions. The intentionally introduced magnesium doping of the p-type cladding layer is regarded as the principle cause of this aging. In this case, even during the epitaxy process when growing a GaP window layer, which is carried out at high temperatures, diffusion of the Mg doping atoms along the concentration gradient toward the active layer may occur.
Aging phenomena also occur during the operation of the light-emitting diodes.
One approach for combating the aging problem is to reduce the diffusion of the Mg doping atoms from the p-doped cladding layer into the active layer. With regard to the longest possible lifetime of the light-emitting diodes, it is desirable to prevent the magnesium diffusion to the greatest possible extent.